This invention relates to an improvement of a steering wheel apparatus, and more particularly to an apparatus of the type having a power transmission mechanism for associating a steering column side to a steering pad including switches such as button switches displayed as to keep the steering pad in a stationary state even when the steering wheel is rotated so that difficulties in operating switches and seeing the display due to the rotation of the steering pad which rotate together with the steering wheel can be prevented.
Heretofore, there is known a steering wheel apparatus having a power transmission mechanism of this type as shown in FIGS. 1 and 2.
In the drawings, a steering shaft 1 is provided with a boss 3 which is fixedly attached to a boss plate 2a of a steering wheel 2. Boss 3 is fastened to the steering shaft 1 by a nut 4. A pad base 7 of a steering pad 6 having push button switches 5 and display thereon is rotatably fitted on the boss 3 and a C-ring 8 is provided in order to prevent the pad base 7 from coming off.
At more than two places in the steering column side, fixing pins 9 having slant surfaces 9a at the foremost end portions are reciprocally received by pin holders 10. A spring 11 is stretched between each of the fixing pins 9 and each of the pin holders 10, so that the fixing pin 9 is biased toward the pad base 7.
The pad base 7 is formed with a recess 7a in the position opposite to the pin holder 10. The foremost end portion of the fixing pin 9 is fitted in said recess 7a. Because of said fitting, rotation of the steering pad 6 is prevented.
The boss plate 2a is designed to be rotated transverse to the fixing pin 9. The boss plate 2a is formed with a slant surface 2b at the portion which contacts the fixing pin 9, so that when the boss plate 2a hits the fixing pin 9, the fixing pin 9 can be easily pushed into the pin holder 10 through the slant surface 9a thereof.
Because of the above arrangement, when the fixing pin 9 is pushed into the pin holder 10 by the boss plate 2a, the steering wheel 2 becomes rotatable through that portion. However, since at least one end of the fixing pins 9 are fitted in the recesses 7a of the pad base 7 at other portions, the steering pad 6 is normally kept stationary in a predetermined position, even when the steering wheel 2 rotates.
However, in a steering wheel apparatus of the above type, since the respective parts of the apparatus are required to be mounted on the steering shaft in order, the mounting efficiency is poor. Also, a constant attention is required from the initial stage of the mounting operation in order to place the steering pad 6 in the right position.
Furthermore, since it is usual practice that a lever combination switch is placed in a position far inside than the steering wheel 2, when the lever combination switch becomes out of order, the whole steering wheel apparatus is required to be dismantled for repairing, and much time and labor are required for it.
Another problem in said conventional apparatus is in a connecting device between the switches 5 and display on the steering pad 6, and the corresponding circuits at the vehicle body side, since the rotary boss plate 2a is interposed therebetween. In other words, a conductive material formed of slip ring and stationary connecting element are required for the purpose of passing the current through the boss plate 2a. However, in order to replace or repair the conductive material, it is required to dismantle the power transmission mechanism for maintaining the steering pad in a stationary state even when the steering wheel is rotated and it is much time and labor consuming.
Furthermore, a serious attention should be invited to the fact that when the fixing pins 9 become difficult to move, the steering wheel 2 will feel heavy.
Although the steering pad 6 does not rotate and is kept stationary as mentioned above, everytime the boss plates 2a transverse the fixing pin 9 during the rotation of the steering wheel 2, the fixing pin 9 is urged to hit the pad base 7 due to the biasing force of the spring 11. Therefore, such inconveniences as that hitting impact is transmitted to the driver, hitting sound is generated and that an unpleasant feeling is created since the rotary loads of the steering wheel 2 are increased every time the slant 2b of the boss plate 2a hits the slant surface 9a of the fixing pin 9, thereby jeopardizing smooth operation of the steering wheel.